Answers

Looks like Mugwort (Artemisia vulgaris). It looks slightly variagated so could have been planted as the cultivar 'Oriental Limelight'. Interesting plant as it's one of the relatively few wind pollinated members of the daisy family. Its probably of not much interest as a garden plant though being wind pollinated, the florets (flower clusters) are reduced and are not showy at all so I will leave that decision to you.

Perhaps I should blame our slugs and snails. I reckon we have more grams of mollusc per cubic metre than anywhere except the home of African Land Snails. Things I used to be able to grow relatively easily in Herts just disappear overnight here.
Theory 2 - it rots in our extremely wet winters?

In a blender with water and a little olive oil and organic soap, strain it through cheesecloth, then spray it on. I don't recommend it for use on edibles, because it is poisonous to people, but no long term environmental effects, because it's very biodegradable. Sachets of dried leaves make good organic "mothballs", too.

Herb scissors? Never heard of them, sound fantastic, wonder where I can get some. Anything that saves all that faffing about chopping them rather inefficiently with a knife...
This plant can be used with lavender and sage to make a good clothes moth repellent too but should be dried first.

Just google multi-bladed herb scissors Bamboo - loads of hits, Amazon amongst others.......strangely not Lakeland though. I saw them somewhere like Aldi, Lidl or Netto on one of their special offers and stupidly didn't grab them.